Battery powered electric traction system

ABSTRACT

A speed controlled electric traction system comprising a direct current compound electric motor having means for controlling its speed from zero up to its maximum value with a minimum energy loss on the speed regulation. The means for controlling the speed of the motor comprise a rheostat in series with the shunt field windings of the motor and linked to a voltage controller in series with the series field winding and armature of the motor. The voltage controller can be one of a number of different types such as a rheostat, a potentiometer allied to a controlled rectifier or a potential dividing switch arrangement acting on the individual cells of the battery. The voltage controller of the armature circuit and the rheostat of the shunt winding are linked together and to an operating member such that as the motor is controlled from standstill the maximum voltage is applied to the shunt winding as the voltage on the armature winding is progressively increased up to a maximum value, and thereafter the voltage on the armature winding is maintained at a maximum while the voltage on the shunt field winding is progressively reduced until the motor attains its maximum speed.

United States Patent 1 Brusaglino 1 May 29,1973

[54] BATTERY POWERED ELECTRIC TRACTION SYSTEM [73] Assignee: FiatSocieta per Azioni, Turin, Italy [22] Filed: Oct. 28, 1971 [21] Appl.No.: 193,290

[30] Foreign Application Priority Data UNITED STATES PATENTS 2,519,1188/1950 Curtis ..318/338 3,569,809 3/1971 Comer ..318/338 3,388,3066/1968 Koppelmann.... ..318/338 3,280,397 10/1966 Bruns r ..318/3382,911,580 11/1959 Gould ..3l8/338 3,546,548 12/1970 Wouk ..3l8/376Primary ExaminerBernard A. Gilheaney Assistant Examiner-Thomas LangerAttorney Richard C. Sughrue. Gideon Franklin Rothwell, Robert V. Sloanet al.

[57] ABSTRACT A speed controlled electric traction system comprising adirect current compound electric motor having means for controlling itsspeed from zero up to its maximum value with a minimum energy loss onthe speed regulation. The means for controlling the speed of the motorcomprise a rheostat in series with the shunt field windings of the motorand linked to a voltage controller in series with the series fieldwinding and armature of the motor. The voltage controller can be one ofa number of different types such as a rheostat, a potentiometer alliedto a controlled rectifier or a potential dividing switch arrangementacting on the individual cells of the battery. The voltage controller ofthe armature circuit and the rheostat of the shunt winding are linkedtogether and to an operating member such that as the motor is controlledfrom standstill the maximum voltage is applied to the shunt winding asthe voltage on the armature winding is progressively increased up to amaximum value, and thereafter the voltage on the armature winding ismaintained at a maximum while the voltage on the shunt field winding isprogressively reduced until the motor attains its maximum speed.

Patented May 29, 1973 3,736,482

4 Sheets-Sheet 1 flI IH Patented May 29, 1973 4 Sheets-Sheet 2 PatentedMay 29, 1973 4 Sheets-Sheet 3 Patented May 29, 1973 4 Sheets-Sheet 4BATTERY POWERED ELECTRIC TRACTION svsTE BACKGROUND OF THE INVENTION Thepresent invention relates to a battery powered electric traction systemespecially for motor vehicles, in which the speed is controlled by meansof adjustment to an electric motor of the compound excitation type. Thisis effected in part by means of a speed regulating rheostat in serieswith the shunt winding and operated by the accelerator pedal or by asuitable hand lever.

Electric traction systems of the above type, powered by a battery suchas an accumulator, are already known, and one of the disadvantages ofknown systems is the power loss involved in speed regulation.

Electric traction systems of this type in which the power loss on speedregulation has been reduced are also known, such systems have advantagesover the unmodified systems as far as general performance is concernedin that the energy dissipated by the speed regulating device may beregarded as substantially negligible. Some of these systems also havethe advantage of dynamic braking by the motor similar to that of thermalengines, and the added advantage of energy regeneration with thisbraking effect.

On the other hand, in previously known systems, the velocity of theengine cannot be allowed to fall below a predetermined speed, whichcorresponds to maximum excitation, and for this reason the known systemshave required gears and a clutch in the same way as internal combustionengines.

It would be desirable, however, to provide a battery powered electrictraction system which would have the advantages of energy regenerationand dynamic braking, and which would in addition make it possible todispense with gears and clutch, thereby simplifying the structure of ithe system, reducing the manufacturing costs, and increasing thereliability of operation of the traction system.

SUMMARY OF THE INVENTION According, therefore, to the present invention,there is provided a battery powered electric traction systemcharacterized in that it comprises a direct current compound electricmotor, a rheostat in series with the shunt excitation field winding ofthe motor, a voltage regulating device in circuit with the armature ofthemotor, the voltage regulating device being linked to the saidrheostat, an operating member for the rheostat and the voltageregulating device, the operating member being movable between a restposition corresponding to deenergization of the motor, and a secondposition corresponding to maximum speed of the motor, the connectionbetween the rheostat and the regulating device being such that as theoperating member is moved away from the rest position the voltageregulating device first causes the voltage in the armature circuit toincrease progressively from nil to the maximum provided by the battery,whilst the rheostat maintains the voltage in the shunt winding constantand at a maximumvalue, and subsequently the voltage regulating devicekeeps the voltage in the armature circuit at the said maximum level,whilst the rheostat progressively reduces the voltage in the shuntwinding, and means for maintaining the armature circuit closed evenwhenthe operating member is returned to its rest position as long as thespeed of the motor remains above a predetermined value.

Various other features and advantages of the present invention willbecome apparent from a consideration of the following description withreference to the accompanying drawings which is given purely by way ofnon limiting example.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic circuit diagramof an electric traction system constructed as a first embodiment of theinvention;

FIG. 2 is a circuit diagram of an electric traction system constructedas a second embodiment of the invention;

FIG. 3 is a circuit diagram of an electric traction system constructedas a third embodiment of the invention;

FIG. 4 is a circuit diagram of a variant of the embodiment of theinvention illustrated in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference now to FIG. 1which illustrates a first embodiment of the invention, there is shown abattery 2 which is arranged to supply the current for the armature andthe series field winding, and also for the shunt field winding of adirect current compound electric motor 3, the battery may be anaccumulator having a plurality of cells, or may, for example, be aplurality of accumulators depending on the power requirements of themotor. The motor 3 is arranged as a traction motor for a motor vehicle,and comprises an armature 4, a shunt excitation or field winding 6 and aseries excitation or field winding 8.

A rheostat 10 controls the current flowing through the shunt excitationwinding 6 and a rheostat 12 controls the current flowing through thearmature and the series excitation winding 8. An accelerator pedal 14controls the angular position of a bell-crank lever 16 which is pivotedat 18 to a point fixed to the chassis of the vehicle. The bell-cranklever 16 is connected to a rod 20 which is coupled to the wiper arm ofthe rheostat 10. The rod 20 has an extension 22 which is connected tothe wiper arm of the rheostat 12 so that both rheostats are controlledsimultaneously.

Both the rheostat l0 and the rheostat 12 are of the same type, and eachconsists of a wiper arm carrying a brush, 24 and 26 respectively, andpivoted respectively at 28, 30. The brushes 24 and 26 slide along rowsof contacts 32, 34 and 36, 38 respectively. The contacts 32, 34, 36 and38 are arranged in an arc of a circle and are connected to respectivegroups of series resistors, 40 and 42. The brushes 24 and 26 26 are alsoconnected to the external circuit by means of flexible conductors, 44and 46 respectively. A return spring (not illustrated) is arranged incontact with the pedal 14 so that when the pedal is not operated itkeeps both the brushes 24 and 26 in the position of maximum clockwiserotation when viewed as shown in Fig. 1.

The rheostat 10 comprises a long contact 32 corresponding to the firstsection of travel of the brush 24; this contact 32 is connected directlyto the positive pole of the battery 2 and extends for just over half ofthe are occupied by the row of contacts, of the rheostat 10. The otherhalf of the row of contacts is subdivided into equal short contracts 34of which four are shown in FIG. 1; each of the contacts 34 is connectedbetween successive series resistors 40 arranged in series with thepositive pole of the accumulator 2. Movement of the brush 24 from therest position therefore successively switches in the resistors 40 aseach of the contacts 34 is reached in turn. The brush 24 is connected toa flexible conductor 44 which, in turn, is connected to the shuntexcitation windings 6 and hence to earth.

The rheostat 12 similarly comprises several short contacts 36 (again,four of which are shown in FIG. 1), however, in this case they arelocated along the first section of travel of the brush 26 and arecoupled to series connected resistors 42 such that as the brush is movedanti-clockwise (as seen in FIG. 1) from its rest position, the resistors42 are successively switched out of the circuit. The rheostat 12 alsohas a long contact 38, extending for just over half of the total lengthof the row of contacts. The brush 26 is connected to a flexibleconductor 46 which, in turn, is connected to a control switch 48 andthence to the positive pole of the battery 2; the long contact 38 isdirectly connected to the series excitation field windings 8 and thenceto the armature 4 of the motor 3.

The wiper arm which carries the brush 26 of the rheostat 12 also carriesa small catch 50 which is arranged to project through an opening 52 inthe housing 54 of the rheostat l2 and to open the contacts of amicroswitch 56, when the bush 26 is in the rest position, that is theposition at the top in the illustration. When the pedal 14 is operatedthe catch 50 is moved away from the microswitch 56 which thereforecloses and allows current to flow from the battery through the coil 68to close the remote control switch 48 and thereby apply a voltage fromthe battery 2 to the brush 26.

A diode 58 is connected in parallel with the group of series resistors42 for reasons which will be described in detail below.

To the shaft 60 of the motor 3 there is connected a dynamo 62 which isconnected to energize a coil 64 of a relay the contacts 66 of which arein parallel with the contacts of the switch 56.

The speed control device described above operates as follows. In therest position the two brushes 24 and 26 of the rheostats and 12 arerotated clockwise to the position where the brush 26 engages with theend contact 36 and the microswitch 56 is held open by the small catch 50on the wiper arm. The coil 68 is therefore de-energized and the contacts48 are open.

By operating the pedal 14 the small catch 50 is moved away from itsinitial position, thereby closing the switch 56; this excites the coil68 and closes the switch 48 thereby applying voltage to the brush 26from the accumulator 2. Thus current flows through the brush 26, thefirst contact of the row of contacts 36 of the rheostat 12, the entiregroup of series connected resistors 42, the series excitation fieldwindings 8 and the armature 4 of the motor 3. The motor is thusenergized with the armature voltage increasing progressively as thebrush 26 of the rheostat 12 is moved across successive contacts 36 tocut out the successive resistors 42 of the armature circuit, whilst thebrush 24 travels along the long contact 32 thus keeping theshuntexcitation current at a constant and maximum valuesince none of theresistors 40 are connected in the circuit.

When the brush 26 of the rheostat 12 reaches the long contact 38, thearmature 4 of the motor 3 is being fed with the full voltage of theaccumulator 2 since all the resistors42 are switched out of the circuit.Further movement of the accelerator pedal causes the brush 24 of therheostat 10 to start to engage the short contacts 34, thus progressivelyswitching in the resistances 40 thereby reducing the excitation of theshunt winding to increase the speed of the motor 3.

Above a predetermined speed of the motor 3, the dynamo 62 begans togenerate sufficient voltage to excite the relays to close the contacts66 to establish an excitation circuit for the relay 68 which bypassesthe switch 56 so that even if the switch 56 is opened the contacts 48remain closed provided the motor 3 is running fast enough. Thereforewhen, with the vehicle travelling, the accelerator pedal 14 iscompletely released to allow the brush 26 to return to the initial restposition where by means of the catch 50, it opens the switch 56, thearmature current of the motor 3 is not switched off so that dynamicbraking-with energy regeneration is obtained on over run, that is whenthe vehicle is travelling faster than the motor 3 and causing the motorto turn and act as a generator. The armature circuit opens again whenthe relay 64, 66 is de-energized as the speed of the motor falls belowthe said predetermined value. By suitable choice of the calibratingvalue of the relay 64 it is possible to cause the opening of thearmature circuit to coincide with the end of the regeneration of energyfrom the motor to the battery.

During the regeneration phase the diode 58 in parallel with theresistors 42 allows the current to circulate directly from the motor tothe battery without passing through the resistors 42 which wouldotherwise give rise to a voltage decrease.

With reference now to FIG. 2, there will be described a secondembodiment of the invention, which allows a speed control to be effectedwithout the dissipation of power which, in the embodiment of FIG. 1,occurs in the resistors 42 of the rheostat 12 during the first phase ofcontrol of the speed of the motor. In this embodiment there is the samearrangement of the compound motor 3 and of the rheostat 10, but therheostat 12 of FIG. 1 is replaced by a potentiometer 212 and by aprocessor 214, and variousother components which will be described ingreater detail below.

The voltage signal on the brush 26 of the potentiometer 212 is comparedin the-processor 214 with the signal from the tachometric dynamo 62. Asa result of this comparison the processor 214 sends firing signals to acontrolled diode 218 via conductors 216, and quenching signals forswitching off the said controlled diode 218 to a quenching circuit 220,via conductors 222 at a rate in dependence on the relative values of thetwo signals. The alternate switching on and off of the controlled diode218 thus applies current impulses to the motor 3 such that the medianvalue is dependent on the duration and frequency of closing of thecontrolled diode 218. By changing the position of the accelerator pedal14, in the section which operates the variable resistor 213, the timeand duration of firing of the controlled diode are adjusted, withconsequent adjustment of current in the motor 3. This current maytherefore vary between nil and the maximum value allowed by the circuitparameters. At the end of the path of the brush .26 along the resistor213, that is, when the voltageapplied to the engine has almost reachedthe value of thevoltage of the battery, the electronic processor 214energies," via conductors 224, a relay coil 226 which switches on aswitch 228 thereby shortcircuiting the controlled diode 218 and directlyapplying the whole of the battery voltage to the engine.

From this point onwards control of the speed of the motor is transferredto the rheostat which progressively reduces the shunt excitation currentto increase the speed of the motor 3.

At the terminals of the motor there is inserted a diode 230, known as afreewheeP diode, which absorbs the excess voltages which occur at theterminals of the motor at the instants when the controlled diode 218passes from the conduction state to the non-conduction state. Thisreduces the pulses of the current to predictable values.

When the accelerator pedal 14 is released with the vehicle stilltravelling, the electronic processor 214, on the basis of a comparisonof the signals of the potentiometer 212 and the tachometric dynamo 62will keep the remote control switch 228 switched off until the end ofthe energy regeneration phase from the motor to the battery orbatteries.

Hence, in this case, also, the motor can be controlled from standstillup to maximum speed whilst preserving the advantage of energyregenerating dynamic braking and high overall performance, thanks to thevirtual absence of energy dissipating elements in the armature circuitof the motor 3.

With reference now to FIG. 3 a further embodiment of the invention willbe described. The components of this embodiment which are common to theprevious embodiments bear the same reference numerals.

In this embodiment the accumulator 2 is subdivided into a number ofcells 310, 312, 314, 316, connected by commutator switches 318, 320,322, 324 (the purpose of which will be described later), and conductors326, 328, 330, 332, 334, to respective poles of a plurality of relaycontacts 336, 338, 340, 342. The coils operating the relay contacts 336,338, 340, 342 respectively are excited by a small auxiliary battery 352via the contacts of a plurality of microswitches 344, 346, 348, 350,which are progressively switched by a sector 354 controlled by the rod20, 22 upon depression of the accelerator pedal 14 between its restposition and approximately half-way along its travel. The microswitches344, 346, 348 and 350 are coupled together in series and the switch 350is connected to one pole of the battery 352 so that as those switchesare progressively switched, the power from the battery 352 isprogressively switched to each of the relays 336, 338, 340, 342 in turn,so that each set of contacts is successively closed at the same timeopening the immediately preceding relay. Therefore a progressivelyincreasing voltage is applied to the armature of the motor 3, toprogressively switch in the cells 310, 312, 314, 316 of the battery,until the maximum voltage which can be supplied by the battery isreached.

In this way control of the speed of the motor 3 from standstill to thegreatest excitation of the separate (shunt) field is achieved. Up tothis point in the travel of the accelerator 14 the brush 24 of therheostat 10 has been in contact with the contact 32 and so has notswitched in any reduction resistor to the shunt field winding of themotor 3.

If the accelerator is moved further the last microswitch 350 will remainoperated by the sector 354 so that the relay 342 which switches in theentire battery to the armature of the motor 3 is held closed:simultaneously however, the brush 24 starts to switch in the resistors40 in to the independent (shunt) excitation winding, which resistors 40,by reducing the field, increase the speed of the motor 3 as in thepreceding embodiments.

When the accelerator is released while the vehicle is still travelling,the tachometric dynamo 62 keeps the relay 64 energized so that thecontacts 66 are closed, until such time as the speed of the motor 3 hasfallen to a predetermined level. The contacts 66 are connected acrossthe last microswitch 350 so that the relay 342 thus remains energiced,and the armature circuit is kept closed thereby allowing theregeneration of energy from the motor to the battery or batteries. Bysuitable choice of the calibration value of the relay 64 it is possibleto make the opening of the armature circuit coincide with the end ofenergy regeneration, as in the preceding embodiments.

Again the speed of the motor can be controlled between its maximumspeed, right down to zero while preserving the advantage of dynamicbraking with energy regeneration and higher overall efficiency of thesystem due to low energy loses in the circuit.

In this embodiment of the invention it will be appreciated that there isan intrinsic non-uniformity of utilization of the cells 310, 312, 314,316 of the battery, since the first cell of the battery is utilized forthe greater part of the time and will therefore discharge more rapidlythan the later ones, which are only called into use at higher speeds.This disadvantage, however, only concerns the range of the lowest speedsand not the whole operating range of the motor since the whole of thebattery is connected for the upper half of the speed range. In order toavoid this disadvantage, even though it is limited, there have beenprovided commutator switches 318, 320, 322, 324 which are operatedsimultaneously by a coil 356, powered by the auxiliary battery 352 andcontrolled by a switch 358, in order to reverse the order in which thecells 310, 312, 314, 316 are switched into the circuit so as to renderutilization of these cells more uniform. The switch 358 may be operatedmanually or else by means of some suitable automatic device (not shown).

Finally, FIG. 4 illustrates a variant of the embodiment of the inventionjust described. This embodiment differs from the embodiment of FIG. 3 byhaving the control circuit 10 of the shunt winding 6 supplies from theterminals of the armature circuit of the motor (node 410) instead offrom the terminals of the whole battery (node 360) in FIG. 3.

In this case therefore, the voltage applied to the terminals of theshunt winding undergoes the same changes as that of the armature, thatis, in the first control phase, as the accelerator is moved from therest position, both the voltage of the armature and that of the shuntfield winding are varied simultaneously from the nil value to that ofthe battery. This variant can have some advantages in certain cases inwhich it is wished to restrict the static torque of the engine.

I claim:

1. A battery powered electric motor system comprising in combination:

a direct current compound electric motor battery means for supplyingpower to said motor,

a rheostat in series with the shunt field winding of said compoundelectric motor,

a voltage regulating device in circuit with the armature and seriesfield winding of said compound electric motor, said voltage regulatingdevice being linked to said rheostat for adjusting movement therewith,

an operating means for adjusting said rheostat and said voltageregulating device, said operating means being movable between a restposition corresponding to de-energization of said motor, and a secondposition corresponding to maximum speed of said motor, said rheostat andsaid voltage regulating device being connected to said operating meanssuch that a said operating means is moved from said rest positiontowards said second position said rheostat maintains said shunt fieldwinding at maximum voltage while said voltage regulating device suppliessaid armature circuit with a progressively increasing voltage up to themaximum provided by said battery whereafter, on further movement of saidoperating means toward said second position said voltage regulatingdevice maintains said armature circuit at said maximum value while saidrheostat progressively reduces the voltage of said shunt field windinguntil said motor obtains its maximum speed,

first circuit means for maintaining said motor energized when saidoperating means is returned to said rest position while said motor isrunning, as long as the speed of said motor remains above apredetermined value, and

second circuit means for directly supplying power from said motor tosaid battery means when said operating means is returned to said restposition while said motor is running and as long as the speed of saidmotor remains above a predetermined value.

2. The battery powered electric motor system of claim 1 wherein saidvoltage regulating device is another rheostat connected between saidbattery and said armature circuit of said motor and said second circuitmeans includes a diode connected across the terminals of said otherrheostat to allow the passage of reverse current from said motor to saidbattery to by pass the resistance of said rheostat.

3. The battery powered electric motor system of claim 1 wherein saidfirst circuit means for maintaining said motor energized when saidoperating means is returned to said rest position while said motor isrunning as long as the speed of said motor remains above a predeterminedvalue, comprises a relay controlled by a dynamo driven by said motor,said relay controlling a separate supply circuit between said armaturecircuit and said battery.

1. A battery powered electric motor system comprising in combination: adirect current compound electric motor battery means for supplying powerto said motor, a rheostat in series with the shunt field winding of saidcompound electric motor, a voltage regulating device in circuit with thearmature and series field winding of said compound electric motor, saidvoltage regulating device being linked to said rheostat for adjustingmovement therewith, an operating means for adjusting said rheostat andsaid voltage regulating device, said operating means being movablebetween a rest position corresponding to de-energization of said motor,and a second position corresponding to maximum speed of said motor, saidrheostat and said voltage regulating device being connected to saidoperating means such that a said operating means is moved from said restposition towards said second position said rheostat maintains said shuntfield winding at maximum voltage while said voltage regulating devicesupplies said armature circuit with a progressively increasing voltageup to the maximum provided by said battery whereafter, on furthermovement of said operating means toward said second position saidvoltage regulating device maintains said armature circuit at saidmaximum value while said rheostat progressively reduces the voltage ofsaid shunt field winding until said motor obtains its maximum speed,first circuit means for maintaining said motor energized when saidoperating means is returned to said rest position while said motor isrunning, as long as the speed of said motor remains above apredetermined value, and second circuit means for directly supplyingpower from said motor to said battery means when said operating means isreturned to said rest position while said motor is running and as longas the speed of said motor remains above a predetermined value.
 2. Thebattery powered electric motor system of claim 1 wherein said voltageregulating device is another rheostat connected between said battery andsaid armature circuit of said motor and said second circuit meansincludes a diode connected across the terminals of said other rheostatto allow the passagE of reverse current from said motor to said batteryto by pass the resistance of said rheostat.
 3. The battery poweredelectric motor system of claim 1 wherein said first circuit means formaintaining said motor energized when said operating means is returnedto said rest position while said motor is running as long as the speedof said motor remains above a predetermined value, comprises a relaycontrolled by a dynamo driven by said motor, said relay controlling aseparate supply circuit between said armature circuit and said battery.